The present invention relates to a Method for Forming a Resist Pattern of Magnetic Device.
With the trend to a larger capacity and a smaller size of hard disk drives (HDD), heads are required to have a higher sensitivity and a larger output. To meet these requirements, strenuous efforts have been made to improve the characteristics of GMR heads (Giant Magneto-Resistive Head) currently available on the market. On the other hand, intense development is under way for a tunnel magneto-resistive head (TMR head) which can be expected to have a resistance changing ratio twice or more higher than the GMR head.
Generally, the GMR head differs from the TMR head in the head structure due to a difference in a direction in which a sense current is fed. A head structure adapted to feed a sense current in parallel with a film surface, as in a general GMR head, is referred to as a CIP (Current In Plane) structure, while a head structure adapted to feed a sense current perpendicularly to a film surface, as in the TMR head, is referred to as a CPP (Current Perpendicular to Plane) structure. Since the CPP structure can use a magnetic shield itself as an electrode, it is essentially free from short-circuiting between the magnetic shield and a device (defective insulation) which is a serious problem in reducing a lead gap in the CIP structure. For this reason, the CPP structure is significantly advantageous in providing a higher recording density.
Other than the TMR head, also known as a head in CPP structure is, for example, a CPP-GMR head which has the CPP structure, though a spin valve film (including a specular type and dual spin valve type magnetic multilayer films) is used for a magneto-resistive device.
Any type of CPP-based heads has an upper electrode and a lower electrode for supplying a current to a magneto-resistive layer formed on a base, formed on the top (opposite to the base) and on the bottom (close to the base) of the magneto-resistive layer, respectively. The CPP-based head comprises an insulating layer for limiting a current path between the upper electrode and lower electrode is arranged around a main layer (for example, a tunnel barrier layer in a TMR head) of the magneto-resistive layer. The limited current path substantially matches an effective region for detecting a magnetic field from a magnetic recording medium. A TMR head is disclosed as an example of the CPP-based head in JP-A-2001-23131 corresponding to U.S. Pat. No. 6,473,257. Generally, Al2O3 or SiO2 is used as a material for the insulating layer. Also, it is often the case that a magnetic head is generally provided with magnetic domain control layers on both sides of a magneto-resistive layer in the track width direction, irrespective of whether the magnetic head is in CPP structure or in CIP structure (including an LOL structure, later described). The magnetic domain control layers apply a biasing magnetic field (a so-called vertical bias) to a free layer, which forms part of the magneto-resistive layer, for controlling magnetic domains.
For manufacturing a conventional CPP-based head as disclosed in JP-A-2001-23131, a lift-off method is typically used. Specifically, a resist pattern for lift-off is formed on constituent layers, which make up a magneto-resistive layer, formed on a substrate, and the constituent layers are patterned by dry etching such as ion milling or the like using the resist pattern as a mask. Then, with the presence of the resist pattern, an insulating layer (or a laminate of an insulating layer and a metal layer (magnetic domain control layer)) is deposited, followed by removal of the resist pattern and the overlying insulating layer (or the laminate of the insulating layer and metal layer (magnetic domain control layer)), thereby forming the insulating layer around the constituent layers as well as forming the magnetic domain control layers on both sides of the constituent layers in the track width direction.
Subsequently, the upper electrode is formed. Generally, for reasons of the manufacturing process, the base formed with the magneto-resistive layer is placed in the atmosphere after the magneto-resistive layer is formed and before the upper electrode is formed. In this event, for preventing the top surface of the magneto-resistive layer from being oxidized in the air to damage the characteristics of the magneto-resistive layer such as an MR ratio, a non-magnetic metal layer, referred to as a cap layer, is previously formed as a protection film on the top surface of the magneto-resistive layer. For example, Ta, Ru, Rh, Au, Pt, Ag, Pd, Ir, Cu or the like is used for the non-magnetic metal layer. In the CPP-based head, the upper electrode is electrically connected to the magneto-resistive layer through the non-magnetic metal layer. The non-magnetic metal layer is formed on the top of the constituent layers, and is patterned by the ion milling or the like together with the other constituent layers.
In the CPP-based head, since a current is applied to the magneto-resistive layer through the upper electrode and non-magnetic metal layer, it is necessary to maintain a good electrical contact between the upper electrode and non-magnetic metal layer to provide a lower resistance. However, since Ta, Ru, Rh, Au, Pt, Ag, Pd, Ir, Cu, or the like may be used for the non-magnetic metal layer, the surface of the non-magnetic metal layer is oxidized in the air, or O2, H2O and the like adsorb on the surface of the non-magnetic metal layer when the base, formed with the magneto-resistive layer and non-magnetic metal layer, is placed in the atmosphere. Thus, if another layer such as the upper electrode is formed on the non-magnetic metal layer as it is, a good electrical contact cannot be maintained between the upper electrode and the non-magnetic metal layer. To address this problem, the surface oxide film is removed from the non-magnetic metal layer by dry etching (including general dry processes such as sputter etching, ion beam etching or the like) within the same vacuum chamber in which the upper electrode and the like are deposited, prior to the formation of another layer such as the upper electrode on the non-magnetic metal layer. Conventionally, the dry etching has been performed using etching particles which do not form clusters, with an incident angle of the etching particles being set in a direction normal to the surface of the base.
Another known CIP-based head has an LOL (lead overlay) structure (for example, see JP-A-2000-99926). The LOL structure comprises a magneto-resistive layer such as a spin valve film, and two upper electrodes formed on the side of the top surface of the magneto-resistive layer for applying a current to the magneto-resistive layer, wherein one of the upper electrodes has a portion overlapping with a portion of the magneto-resistive layer on one side in a plane direction, while the other of the upper electrodes has a portion overlapping with a portion of the magneto-resistive layer on the other side in the plane direction, so that the two electrodes are spaced away from each other in the plane direction. In other words, the LOL structure comprises a pair of lead layers for applying a current to an effective region of the magneto-resistive layer in a direction substantially parallel with a film surface thereof, wherein the pair of lead layers include an overlay which extends onto a portion of the magneto-resistive layer on the top surface side (opposite to the base) of the magneto-resistive layer.
A lift-off method is typically used as well for manufacturing such an LOL-based head, as is the case with the CPP-based head. Specifically, a resist pattern for lift-off is formed on constituent layers, which make up a magneto-resistive layer, formed on a substrate, and the constituent layers are patterned by dry etching such as ion milling or the like using the resist pattern as a mask. Then, with the presence of the resist pattern, an insulating layer (or a metal layer (magnetic domain control layer)) is deposited, followed by removal of the resist pattern and the overlying insulating layer (or the metal layer (magnetic domain control layer)), thereby forming the insulating layer around the constituent layers (in the LOL structure, around an end opposite to the rear end (end opposite to ABS (air baring surface) in the height direction) as well as forming the magnetic domain control layers on both sides of the constituent layers in the track width direction.
Subsequently, the lead layers are formed. Generally, for reasons of the manufacturing process, the base formed with the magneto-resistive layer is placed in the atmosphere after the magneto-resistive layer is formed and before the lead layers are formed. In this event, for preventing the top surface of the magneto-resistive layer from being oxidized in the air to damage the characteristics of the magneto-resistive layer such as an MR ratio, a non-magnetic metal layer, referred to as a cap layer, is previously formed as a protection film on the top surface of the magneto-resistive layer, as is the case with the CPP-based head. For example, Ta, Ru, Rh, Au, Pt, Ag, Pd, Ir, Cu or the like is used for the non-magnetic metal layer. In the LOL-based head, the lead layers are electrically connected to the magneto-resistive layer through the non-magnetic metal layer. The non-magnetic metal layer is formed on the top of the constituent layers, and is patterned by the ion milling or the like together with the other constituent layers.
In the LOL-based head, since a current is applied to the magneto-resistive layer through the lead layers and non-magnetic metal layer, it is necessary to maintain a good electrical contact between the lead layers and non-magnetic metal layer to provide a lower resistance. However, since Ta, Ru, Rh, Au, Pt, Ag, Pd, Ir, Cu, or the like may be used for the non-magnetic metal layer, the surface of the non-magnetic metal layer is oxidized in the air, or O2, H2O and the like adsorb on the surface of the non-magnetic metal layer when the base, formed with the magneto-resistive layer and non-magnetic metal layer, is placed in the atmosphere. Thus, if other layers such as the lead layers are formed on the non-magnetic metal layer as it is, a good electrical contact cannot be maintained between the lead layers and the non-magnetic metal layer. To address this problem, the surface oxide film is removed from the non-magnetic metal layer by dry etching (including general dry processes such as sputter etching, ion beam etching or the like) within the same vacuum chamber in which the lead layers and the like are deposited, prior to forming other layers such as the lead layers on the non-magnetic metal layer. Conventionally, the dry etching has been performed using etching particles which do not form clusters, with an incident angle of the etching particles being set in a direction normal to the surface of the base, as is the case with the CPP-based head.
In a variety of applications other than the manufacturing of magnetic heads, a lift-off based pattern forming method is used.
However, in the conventional manufacturing method for manufacturing the aforementioned CPP-based head and LOL-based head, the surface oxide film on the non-magnetic metal layer, redeposits produced during the dry etching such as ion milling, and the insulating layer (or the laminate of the insulating layer and metal layer (magnetic domain control layer)) remain on a peripheral region and the like of the non-magnetic metal layer due to the resist pattern for lift-off which has a shape at cross section including an undercut or an inverse tapered shape at cross section, thereby limiting a path for a current which flows into the magneto-resistive layer to reduce an area which has a good electrical contact. As a result, the magnetic head manufactured by the conventional manufacturing method experiences an increase in a series resistance component of the magneto-resistive device, degraded MR characteristics, degraded frequency characteristics due to a higher resistance of the head, and the like. It is difficult to reduce the dimensions of the undercut or the like of the resist pattern for lift-off to predetermined dimensions or less in order to avoid producing burrs and the like during the lift-off. Thus, when a magneto-resistive device is reduced in size for increasing a recording density, the resulting magneto-resistive device has a significantly reduced area which makes an electrically good contact to strictly limit a path for a current which flows into a magneto-resistive layer, thereby notably affecting the magneto-resistive device due to the degraded MR characteristics, degraded frequency characteristics associated with a higher resistance of a head, and the like. These aspects will be described later in greater detail in the description of a comparative example which is compared with the present invention.
Also, as mentioned above, the magnetic domain control layer remains as well on peripheral regions (here, peripheral regions on both sides in the track width direction) of the non-magnetic metal layer due to the undercut or the like of the resist pattern for lift-off. This causes a portion of the magnetic domain control layer to also be piled on the magneto-resistive layer. Consequently, part of a biasing magnetic field from the magnetic domain control layer passes through the piled portions of the magnetic control layers on both sides to bypass the free layer without entering the free layer. This results in a lower vertical biasing effect to the free layer by the magnetic domain control layer, thereby failing to sufficiently control the magnetic domains of the free layer. Since it is difficult to reduce the dimensions of the undercut or the like of the resist pattern for lift-off to predetermined dimensions or less as mentioned above, a reduction in the dimensions of the magneto-resistive device for a higher recording density would significantly narrow down the distance between the piled portions of the magnetic domain control layers on both sides, thereby notably affecting the control for the magnetic domains of the free layer. This aspect will also be described later in greater detail in the description on a comparative example which is compared with the present invention.
While a magnetic head manufacturing method has been given as an example for purposes of description, troubles can be also caused by the resist pattern for lift-off having the undercut or the like in a lift-off based pattern forming method which is used in a variety of applications other than the manufacturing of magnetic heads. Specifically, troubles may be caused by unwanted products, which can be redeposits during ion milling, a second film formed around a first film, and the like, remaining on a peripheral region an the like of the first film patterned by ion milling or the like using the resist pattern for lift-off as a mask.